Method or process for the expansive burning of clays



May .29, 1934. F. w. B UTTERWORTH ET AL 1,960,571

METHOD on PROCESS FOR THE EXPANSIVE BURNING OF CLAYS Filed April 11',1932 w y E Patented May 29, 1934 UNITED STATES PATENT OFFICE METHOD ORPROCESS FOR THE EXPANSIVE BURNING OF CLAYS Illinois Application April11, 1932, Serial No. 604,538 17 Claims. (Cl. 25156) This inventionrelates to a new and improved method or process for the expansiveburning of clays and to articles produced by such process. Moreparticularly our invention relates to a method by which cellulararticles may be formed of a predetermined size and shape.

We are aware that the expansive burning of clay has been practicedheretofore for the purpose of forming a light aggregate for themanufacture of molded articles. In all such prior processes of which wehave knowledge, however, the aggregate formed is irregular in size andshape. The

clay during the burning expands and even ii formed before burning, theform and size are both materially altered by the expansion which isirregular in character and amount.

It is an object of the present invention to provide a new and improvedmethod for forming articles of a predetermined size and shape by the 2expansive burning of clays.

It is a further object to provide a method whereby the expansion of theclay during the buming may be adequately controlled as to direction andamount.

It is also an object to provide articles of expansively burned claywhich are of a desired size, shape and density. a

"It is an additional object to provide a building block or the likewhich is light, strong, impervious to water. and which has highinsulating'propfities and good sound absorption. 7

It is a further object to provide a method of making and burning suchblocks or the like whereby the time and fuel required for burning arevery materially reduced below that required for usual types of ceramicblocks or tile.

Other and further objects will appear as the description proceeds.

We have shown certain preferred embodiments of our invention in theaccompanying drawing, in which- Figure 1 is a perspective view of oneform of' blank prior to burning;

Figure 2 is a similar view of the same blank after burning;

Figure 3 is a perspective view showing one form of mold or containerused for restraining or limiting the expansion of the blank during theburning process; D

Figure 4 is a transverse section on a reduced scale showing the blankwithin the container before burning Figure 5 is a view similar to Figure4 but showing the blank after burning and Figure 6 is a view similar toFigure 4 but showing a different type of container.

The form of blank shown in Figure 1 consists of a rectangular blank 11of approximately the size and general 'shape which it is desired thefinished brick or block should take. This blank 11 is provided with aplurality of rectangular openings 12 which extend all the waythrough theblank. Under the expansion caused by the heat, the blank tends to swellin all directions and by the use of a container or restraining housingthis swelling is limited in direction, and further the external swellingis definitely limited in amount. It will be seen that the walls aboutand between the openings 12 are substantially the same thickness so thatt e heat will be transmitted substantially uniformly to the materialthroughout the blank. This causes the swelling to be substantiallyuniform and also substantiallysimultaneous. When restrained by thecontainer or housing, the blank will swell to completely fill thecontainerand any further expansion must be eifected by filling up theopenings 12.

As shown in Figure 2, the block 13 is of cellular construction and theopenings 12 are completely closed. Also the size of the block hasslightly increased in each direction.

lg One form of container or housing suitable for carrying out the methodis shown in Figure 3. This container consists of a bottom 14, lateralwalls 15, and a removable cover plate 16. The plate 16 is formedwith'openings 17 which approximate in form and location the openings 12which extend through the blanks 11. The cover 16 is shown held in-placeby lugs 18 and wing nuts 19. The bottom 14 is provided with openingssimilar to the openings 17 of the cover 16 and located in approximatealignment with the openings 1'7. The container is provided with thesupports 20 whichserve to elevate the bottom of the container above thefloor 21 of the kiln or heating chamber in' which the container may beplaced.

In Figure 4 the blank 11 is shown in place in the container, the cover16being fixed in place. The openings 12 are indicated by broken lines.In Figure 5 the section shows the block 13 after burning, thiscompletely filling the container instead of having a clearance on allsides as shown in Figure 4.

Figure 6 indicates a refractory container 22 having a refractory lid orclosure 23. This is shown as containing the blank 11 having the openings12 therethrough'. v

In forming blocks according to our method by the use of a container ofthe character shown in Figures 3, 4 and 5, the blank is affected by theheat both through conduction through the walls of the container and bygases passing through the openings 1'7 in the top and through thebottom, and through the openings 12 in the blanks until these openingshave been filled by the expansion of the material. In the form ofconstruction shown in Figure 6, the blank will be affected solely byheat conducted through the walls of the refractory container. It will beunderstood that the refractory container may be made of any materialadapted to withstand the heat required for burning the block withoutmaterial injury or deformation. The container may beperforated or not,as desired. There is no great amount of strain imparted to the containerby the expansion of the block and consequently no great tensile strengthis required.

It will be understood that the forms of container shown, are merelyillustrative, as in commercial operation it is probable that containerswould be used having a plurality of compartments each of which wouldcontain an individual block. Our process will be describedin connectionwith the making of bricks or building blocks although it will beunderstood that it may be equally well applied to articles of otherforms, shapes and sizes.

The bricks are made in the regular way by any of the regular processesof molding and are dried in the usual way, the only difference beingthat instead of being solid, they are made with voids, 30 to of thevolume of the brick. The amount of voids will vary with different claysand according to the kind of ware to be produced.

After these bricks or blanks which might be called hollow bricks, comefrom the dryhouse with a large percentage of the physically combinedwater evaporated, they are then placed in the fire clay molds or metalmolds just a trifle larger than the dried brick.

The process from that point on radically differs from the ordinaryburning process by which the ware is contracted.

First, although the ware is theoretically dry, there is always somelittle moisture present and it is necessary to' expose it to atemperature slightly in excess of the boiling point in order to be surethat all of the physically combined water has left it. a

Second, the temperature is thenincreased to a point well below thedehydrating and oxidation points.

Third, immediately that the ware has attained the above temperature,- itis put into a temperature appreciably higher than that at which itvitrifies or at which the fluxes melt. The effect of this is to melt thefluxes and at the same time, expand the gases contained in the clay,resulting in a rapid and more or less thorough expansion of the ware.The ware being enclosed in and nearly filling a mold of the ultimatesize and shape of the desired ware, and the clay body being full ofvoids, the expansion goes mainly in one direction; that is, toward thevoids which are either entirely or partially filled up.

Fourth, the ware is kept at this temperature for a very short time,suificiently long to insure a vitrification of all of the partitionsforming the cells in which the gases are trapped, and although the majorpart of the expansion comes quickly, the expansion will continue for anindefinite period if this high temperature is maintained.

Fifth, the ware is then cooled in the regular way, although ourexperience is that due to its cellular properties, etc., it can becooled much quicker without danger than where it is contracted duringthe burning process.

It has been found that the time required for this method of burningafter the physically combined water has been expelled and up to the timeof cooling is often as little as fifteen minutes, dependent upon thecharacter of the clay, the maximum temperature of the hot zone and thenumber and volume of the voids in the unit.

As a specific example, the blank may be placed in a temperature ofapproximately 1000 F. and the temperature gradually raised until intwentyfive minutes it reaches 2000 F. The rise in temperature maycontinue until at the end of forty minutes it reaches a maximum of 2240R, which is maintained for three minutes after which the block is'slowlycooled.

By our method, the amount of expansion can be exactly controlled by thetemperature of the hot zone and the length of time in which the ware isallowed to remain at the high temperature point. Thus, from the samematerial, ware of very great strength and considerable density can bemade; or, ware of little structural strength and extremely cellular canbe manufactured.

' If it is desired to retain somewhat the same outside appearance of theware as though it were burned by the ordinary process, the dry hollowware is made so that there will be very little clearance between it andthe refractory mold; and this side of the mold is not perforated, and bymaintaining this close juxtaposition, the original texture and conditionof the ware is maintaned, even though the expansion is 200%.

Although it seems desirable to form the ware in the usual way asdescribed above, we have found that the following method also producesthe same kind of ware. In the place of the regular molding machinery,the raw shale after being ground to fairly uniform particles, say thatwill pass through a ring and be retained on a. screen with the holes indiameter are coated in a drum or any other apparatus with a coating of arather weak solution of sodium silicate and while wet, these particlesof day are lightly pressed together in the desired form with voids andthe sodium silicate allowed to set, after which the ware is treated inthe same way as formerly described. The sodium silicate will make a bondbetween the particles, holding them together in the desired form andthis bond will not" be destroyed by heat until a temperature is reachedat which another bond. is substituted. By either process the resulting.ware is highly cellular and therefore is very light in weight, it beingquite possible in the same clays and shales to secure 200% expansion;that is, the clay or shale will have been converted into a cellular massthree times its original volume.

This ware, burned in this way, as stated above, can be made sufficientlydense to have high crushing strength and still be cellular or can beexpanded to almost the entire limit into a very lightweight ware withbut little structural strength.

The containers or molds may be knock-down in character or may beslightly tapered to facilitate the removal of the formed blocks. Variousmeans may be used for preventing or limiting adhesion of the formedblock to the container. For example, the interior of the container maybe coated with graphite or a lime wash, or may the heat of the burning,but the non-fusible ashv will serve to prevent adhesion. Sand used inthe mold to prevent adhesion might also aid in,

giving a desired finish to the block, as is customary in various typesof face brick at the present time. As a further method of preventingadhesion and giving a desired surface, a paper or membrane having sandcaused to adhere thereto by an adhesive such as sodium silicate, may beused for lining the container, the paper or membrane being destroyed bythe heat and the sand adhering to the finished block.

blank shown in Figure 1 is also merely illustrative, as a large varietyof forms of blank may be used to meet varying conditions andrequirements. The openings extending through the block may vary in sizeand location, and when the block is burned they may be fully orpartially closed up as desired. For many purposes for which these blocksare adapted it is immaterial, or in some cases desirable, to haveopenings extending through the blocks. In such cases the perforations oropenings through the blank may only partially be filled by theexpansion. In cases where it is desired to have openings through thefinished block which openings are of a definite size and character,collapsible or removable mold members or cores may be placed in thecontainer extending through the blank and remaining in place until theheat treatment is completed.

The amount of expansion permitted upon the outside of the blank willvary as desired. In some cases it may be desirable to limit thisexpansion very closely and force all of the expansion to the interior ofthe block. Such a method of manufacture will tend to give a smoother anddenser surface than where greater exterior surface expansionispermitted. The surface may be treated in various ways as is now known inthe ceramic art by having layers of different types of clay or othermaterial placed on the blanks before burning, in order to give anydesired finish to the surface of the product. The surface color andtexture may be varied by permitting more or less surface oxidationbefore the burning temperature reaches that necessary for causing thecellular expansion. 1 v

The amount of expansion may be controlled by the nature of the materialforming the blank, by its moisture content, by the speed with which theblank is moved through the various heat zones, and by the modificationof the temperatures of these zones. By variation of any or all of theseelements a block of desired lightness and cell size and content may beobtained.

The kiln or furnace in which this burning takes place can be of any typebut in our practice we prefer a tunnel furnace, with the ware movingthrough a hot zone either on cars according to usual tunnel kilnpractice, or on a refractory conveying system. Due to the short time inwhich the ware is in the hot zone (from three to ten minutes), the wareis produced very rapidly and the burning cost greatly reduced over anyother known process.

While we have described and shown various methods of carrying out ourinvention, these are to be understood as illustrative only, as bothmethod and product are capable of wide variation-to meet differingrequirements and we contemplate such changes and modifications as comewithin the spirit and scope of the appended claims.

We claim:

l. The method of making an expanded ceramic product which comprisesforming a ceramic blank, heating the blank to a temperature at which theblank expands to a material extent,

and restraining said expansion.

' 2. The method of making an expanded ceramic product which comprisesplacing a, blank of ceramic material in a container, said blank beingslightly spaced from the container walls and hav ing voids internallythereof, and heating the ceramic material in the container to atemperature at which the material expands to contact It will be furtherunderstood that the form of with the walls of the container.

3. The method of making an expanded ceramic product which comprisesforming a ceramic blank of approximately the size and of the shape ofthe desired product, heating the blank to a temperature and with suchrapidity that the blank expands to a material extent, and restrainingsaid expansion to hold the desired size and shape for the finishedproduct.

4. The method of making an expanded ceramic product which comprisesforming a ceramic blank having voids therein, heating the blank to atemperature at which the material forming the blank expands, restrainingexternal expansion, and permitting internal expansion.

5. The method of making an expanded ceramic product which comprisespartially filling with ceramic material a container closable on allfaces, closing said container and heating the material in the containerto a temperature and with such rapidity that it expands and engages allfaces of the container.

6. The method of making an expanded ceramic product which comprisesforming a ceramic blank having voids therein, heating the blank to atemperature at which the material forming the blank expands, restrainingexternal expansion to an amount such as to bring the blank to the sizeand shape desired for the finished product, and permitting internalexpansion.

'7. The method of making an expanded ceramic product which comprisesforming a ceramic blank having openings extending through the blank,heating the blank to a temperature at which the material forming theblank expands, restraining external expansion and permitting internalexpansion into said openings.

8. The method of making an expanded ceramic 0 product which comprisesforming a ceramic blank having openings extending through the blank,heating the blank to a temperature and with such rapidity that thematerial forming the blank expands, restraining external expansion andpermitting internal expansion into said openings to completely fill saidopenings.

9. The method of making an expanded ceramic product which comprisesforming a ceramic blank, placing the blank in a container with materialbetween the blank and container walls to prevent adhesion of said wallsduring the burriing of the blank, raising the temperature of the blankwhile in the container to such a degree as to cause expansion of theblank forcing it in intimate contact with the container walls, andtherecontainer.

10. The method of' making an expanded ceramic product which comprisesforming a ceramic blank, placing the blank in a substantially closedcontainer having a cubic capacity greater than the cubic solid contentof the blank, and heating the blank in the container to such atemperature as to cause it to expand and fill the container.

11. The method of making an expanded ceramic product which comprisesforming a blank having approximately the size and outer contour of thedesired product, placing it in a substantially closed container of thesize and contour of' the desired product, and heating the blank andcontainer to such a temperature that the blank expands to contact withall walls of the container.

12. The method of making an expanded ceramic product which comprisesplacing ceramic material in a container of the size and shape of thedesired finished product, heating the material in the container to atemperature to drive off physically combined water, slowly raising thetemperature to a point somewhat below the dehydration and oxidationpoints, and quickly raising the temperature to a point at which thefluxes in the material melt and the material expands and vitrifies, theexpansion causing it to engage all walls of the container.

13. The method of making an expanded ceramic product which comprisesplacing ceramic material in a container of the size and shape of thedesired finished product, heating the material in the container to atemperature to drive off physically combined water, slowly raising thetemperature to a point somewhat below the dehydration and oxidationpoints, and quickly raising the temperature to a temperature ofapproximately. 2000 F. or above at which point the fluxes in thematerial melt and the material expands and vitrifies, the expansioncausing it to engage all walls of the container.

14. The method of making an expanded ceramic product which comprisesforming a blank having voids therein and being of approximately the sizeand shape of the desired finished product, enclosing said blank in acontainer having an interior of the size and shape of the finishedproduct, slowly raising the temperature of the blank to a point belowthe melting point of the fluxes in the blank and then quickly raisingthe temperature to the point at which the blank expands and vitrifies tofill the container.

15. The method of making an expanded ceramic product which comprisesforming a blank having voids therein and being of approximately the sizeand shape of the desired finished product, enclosing said blank in acontainer having an interior of the size and shape of the finishedproduct, slowly raising the temperature of the blank to a point belowthe melting point of the fluxes in the blank, then quickly raising thetemperature to the point at which the blank expands and vitrifies tofill the container, maintaining the blank at this temperature for ashort period, and gradually cooling the product.

16. The method of making an expanded ceramic product which comprisesforming a blank having voids therein and being of approximately the sizeand shape of the desired finished product, enclosing said blank in acontainer having an interior of the size and shape of the finishedproduct, slowly raising the temperature of the blank to a point below1300 F., raising the temperature quickly to a point above 1950 F.,maintaining it at such temperature for a short time, and graduallycooling the product.

1'7. The method of making an expanded ceramic product which comprisesforming a blank having voids therein and being of approximately the sizeand shape of the desired finished product, I.

enclosing said blank in a container having an interior of the size andshape of the finished product, slowly raising the temperature of theblank to a point below 1300 F., raising the temperature quickly to apoint above 1950 F., maintaining it at such temperature forapproximately five minutes, and gradually cooling the product.

FRANK W. BU'II'ERWORTH. IVAN N. DOUGH'I'Y. IRL R. CLIN'E.

